I included a few tall images in a recent question I asked on space.se. I thought they would scale to something appropriate, but as they are very tall images, it really didn't. For your information, here is one of them posted here. Can you set a reasonable max height in the CSS for images?
Personally, I don't think it makes sense to impose a global limit. Sometimes you might want a tall image (although I can't think of any specific examples). It's also pretty rare for this to come up. Most images tend to be at the most slightly taller than they are wide, if even that.
I've been visiting MetaSE for a while now, and one thing I've noticed regularly is that Stack Exchange isn't that keen on investing developer time into issues with small radii of effect. If it were common for people to post super tall images, they might do something, but this is the first I've personally seen that's just ridiculous (although I don't spend time on SpaceSE).
To address the point of possible abuse, that definitely is a potential problem, but I don't think an image height limit is going to dissuade a troll. They'll just abuse something else. I've also never seen someone posting an image anywhere near even 20,000px tall, much less 200,000px, and that's including square or landscape images.
Another reason I don't think it makes sense to impose a height limit is because you can pretty easily do it yourself (or do it for someone else). Since it's a definite edge case that images are so much taller than they are wide that they take up too much vertical space, it makes more sense, to me at least, to just "fix" images individually.
Take a look at this Super User post, which has some ways to set the size of the image.
While it doesn't work for this particular image, with Imgur links you can generally add a, m, l, h, etc at the end of the image ID (just before the .png or .jpg extension), to set the rough size.
Or, you can try:
<img src="[url]" height="[nnn]">
Example (500px height):